The present invention relates to a method and an apparatus for cleaning of gas, by means of centrifugal force, from solid or liquid particles suspended in the gas and having a larger density than the gas. The invention is intended for use above all in connection with cleaning of so called crankcase gases, i.e. gases formed in a combustion engine, from particles in the form of oil and/or soot. Alternatively, however, it may be used in other connections.
More closely the invention concerns cleaning of gas in a way such that the gas is conducted through a chamber, which is delimited by a stationary housing, and is caused to rotate in the chamber by means of a rotor kept in rotation around a rotational axis, the particles by upcoming centrifugal force being separated from the gas and thrown towards the stationary housing.
An apparatus for cleaning of gas in this way is known for instance through each one of the patents DE 35 41 204 A1 and DE 43 11 906 A1, which describe cleaning of crankcase gases coming from a combustion engine.
Thus, DE 35 41 204 A1 shows an apparatus of this kind, in which the rotor is formed as a turbine or pump wheel, which is adapted to be brought into rotation by gas to be cleaned entering from below into said chamber. The gas to be cleaned is caused to flow through the turbine or pump wheel from its centre to its periphery, where it leaves the turbine or pump wheel, rotating at the same speed as this wheel. Particles are separated from the gas rotating in the chamber by centrifugal force, and cleaned gas leaves the chamber through an outlet at the upper part thereof. Particles separated from the gas deposit onto the surrounding wall of the chamber, liquid particles coalescing on the surrounding wall and liquid, thereafter, running down it and further out through an outlet situated at the bottom of the chamber.
DE 43 11 906 A1 shows a similar apparatus for cleaning of crankcase gases, in which the rotor is adapted to be driven by means of pressurized lubricating oil coming from the combustion engine, the crankcase gases of which are to be cleaned in the apparatus. The driving lubricating oil is supplied to the rotor at its centre and leaves the rotor through tangentially directed outlets situated at a distance from the rotational axis of the rotor. The rotor constitutes in itself, in this case, a device for cleaning of the driving lubricating oil. The cleaned lubricating oil is released in the lower part of the chamber, through which the crankcase gases shall pass in order to be cleaned, and is returned therefrom to the lubricating oil system of the combustion engine. The crankcase gases are caused to pass axially through a narrow space delimited in the chamber between the rotor and the surrounding stationary housing. Gas rotating in the space is freed from particles suspended therein, which particles deposit onto the inside of the stationary housing, where liquid particles coalesce and liquid thus formed, thereafter, flows towards an outlet.
The two above described known apparatuses for cleaning of crankcase gases have rather a poor efficiency when it comes to separation of particles from a through flowing gas.
The object of the present invention primarily is to accomplish a method of cleaning gases, particularly crankcase gases, which is substantially more effective than the above described gas cleaning methods. It is suggested that a certain previously known technique, other than the one mentioned above for cleaning of crankcase gases, is utilised and improved.
Thus, it is suggested, in accordance with what has initially been said, that
a rotor is kept rotating around a rotatonal axis in a chamber delimited by a stationary surrounding wall, which rotor comprises a stack of conical separation discs arranged coaxially with each other and concentrically with said rotational axis, the separation discs being provided with radially outer surrounding edges,
the gas to be cleaned is conducted through interspaces formed between the separation discs from gas inlets to gas outlets situated at differently large distances from the rotational axis of the rotor, so that the gas is caused to rotate with the rotor and the particles, as a consequence of upcoming centrifugal force, are brought into contact with the insides of the separation discs, and
separated particles by the rotation of the rotor are caused first to move a distance in contact with the separation discs substantially along the generatrices thereof towards said surrounding edge and then are thrown from the separation discs towards said surrounding wall.
Technology of this kind is previously known for instance through U.S. Pat. No. 2,104,683 and U.S. Pat. No. 3,234,716. In each one of these patent specifications it is described how particles having been brought into contact with the insides of the conical separation discs are moved by means of centrifugal force towards the surrounding edges of the separation discs.
U.S. Pat. No. 2,104,683 describes (with reference to FIG. 2) that particles in the areas of the radially outermost parts of the separation discs are influenced substantially only by centrifugal forces and move substantially along the generatrices of the separation discs, i.e. in straight paths along radii drawn from the rotational axis of the rotor, whereas particles in the areas of the radially inner parts of the separation discs also and to a very large degree are influenced by flowing gas and, thereby, move in a direction forming an angle with these generatrices. The flowing gas may move substantially freely between the separation discs and may adopt a flow direction determined by among other things the speed by which the gas enters the interspaces between the separation discs and the degree of influence from the rotating separation discs.
U.S. Pat. No. 3,234,716 describes (with reference to the FIGS. 3 and 4) how particles are separated in the interspaces between conical separation discs. After having got into contact with the insides of the separation discs the separated particles move substantially radially outwardly from the rotational axis of the rotor towards the surrounding edges of the separation discs.
For improvement of the separation efficiency upon use of this previously known technique it is suggested according to the invention
that separated particles moving in contact with the separation discs substantially along the generatrices thereof are caught and conducted, together with other particles caught in a similar way, further towards the said surrounding edges of the separation discs along paths forming an angle with said generatrices and
that separated particles are caused to leave said paths and are thrown from the separation discs substantially only in limited areas spaces from each other along the surrounding edges of the respective separation discs.
The improvement hereby obtainable is that particles which have once been separated from the gas have increased possibilities in comparison with use of the previously known technology to remain separated from the gas and, thus, not to be entrained again by gas flowing at a large velocity through the space through which the particles have to pass on their way from the rotor to the surrounding stationary surrounding wall. Thus, the particles are collected by means of guiding or conducting members, after which they are conducted further on by means of the centrifugal force towards the surrounding edges of the separation discs while being agglomerated or coalesced to larger particles. In an agglomerated form or as relatively large drops the separated particles are then thrown towards the stationary surrounding wall in limited areas distributed along the surrounding edges of the separation discs, whereas between such areas spaces are left for gas flow into or out of the interspaces between the separation discs.
The gas to be cleaned may be brought to flow between the separation discs either in a direction from or in a direction towards the rotational axis of the rotor. It is preferred that the flow is taking place in the direction from the rotational axis, as the flow will then be assisted by a pumping effect of the rotor on the gas. Thereby, no auxiliary means are needed to get the gas to flow through the interspaces between the rotating separation discs. The gas to be cleaned preferably is conducted into the interspaces through an inlet space delimited centrally in the stack of separation discs, whereas cleaned gas is conducted out of the interspaces to an outlet space in said chamber, which surrounds the stack of separation discs.
The invention also concerns an apparatus for cleaning of gas from particles suspended therein. An apparatus of this kind comprises a stationary housing that delimits a chamber and that has a gas inlet to the chamber and a gas outlet from the chamber, and a rotor rotatable around a rotational axis and adapted to bring gas to be cleaned into rotation in the chamber. The apparatus according to the invention is characterised in
that the rotor includes a stack of conical separation discs arranged coaxially with each other and concentrically with the rotational axis of the rotor, said separation discs delimiting between themselves interspaces for through flow of gas,
that at least a first flow space is delimited centrally in the stack of separation discs, which flow space communicates with radially inner parts of the interspaces between the separation discs,
that at least a second flow space is delimited by and between the stack of separation discs and the stationary housing, said second flow space communicating with radially outer parts of the interspaces between the separation discs,
that said first flow space communicates with one and said other flow space communicates with the other one of the gas inlet and the gas outlet, respectively, the apparatus being formed to conduct substantially all gas, which is supplied through the gas inlet to said chamber, through the interspaces between the separation discs, and
that each one of the conical separation discs on its inside is in contact with or is connected with elongated conducting members, each of which extends in an angle with the generatrices of the separation disc from a point at a first distance from the rotational axis of the rotor to a point at a second larger distance from the rotational axis of the rotor, said conducting members for each separation disc ending in the vicinity of the surrounding edge of the separation disc spaced from each other seen along the surrounding edge.
The separation discs may have the form of either complete or frustroms of cones, each separation disc having either one large or several small holes in its central portion for through flow of gas to be cleaned or gas having been cleaned. Such holes in the separation discs form together with the interspaces between the separation discs central parts of one or more inlet or outlet spaces centrally in the stack of separation discs. For reasons having been given before it is preferred that the flow space centrally in the stack of separation discs communicates with the inlet and that the flow space surrounding the separation discs communicates with the gas outlet, so that gas to be cleaned is caused to flow in a direction from the rotational axis of the rotor through the interspaces between the separation discs.
In operation of an apparatus according to the invention liquid particles depositing on the surfaces of the separation discs will coalesce to larger drops, which when they reach said conducting members and move along these will coalesce to even larger drops. The liquid drops leaving the separation discs are, therefore, substantially larger than the liquid particles contained in the not yet cleaned gas. Even solid particles depositing on the surfaces of the separation discs will accumulate or be agglomerated to substantially larger units, before they are thrown away from the surrounding edges of the separation discs.
Since particles having got into contact with a separation disc will then move substantially along the generatrices thereof, it is suitable that conducting members of the aforementioned kind are distributed around the rotational axis of the rotor and have an extension such that two adjacent conducting members cross one and the same generatrix of the separation disc at points situated at different distances from the rotational axis of the rotor. Hereby, it can be assured that substantially all particles having got into contact with the separation disc are caught by the conducting members and may agglomerate or coalesce with other particles to larger units on or at these conducting members on their way towards the surrounding edge of the separation disc.
The conducting members advantageously are formed such that they can also serve as spacing members between adjacent separation discs. Then, each conducting member along the whole or parts of its extension may bridge the whole distance between two adjacent separation discs. More or less the conducting members will then also determine the flow direction of the gas flowing between the separation discs. Nothing prevents, however, that all or some of the conducting members extend only across part of the axial distance between adjacent separation discs. Preferably, a conducting member is firmly connected with a separation disc.
The stationary housing surrounding the rotor preferably has an outlet at the lower part of the chamber for liquid or sludge having been separated from the contaminated gas and having deposited on the surrounding wall of the chamber.
In an apparatus according to the invention the rotor may be driven by means of any suitable kind of driving device, e.g. an electrically, hydraulically or pneumatically driven motor.